A dangerous heart rate for a child depends heavily on age, because what’s normal for an infant would be alarming in a teenager. In general, a resting heart rate consistently above 200 beats per minute (bpm) in an infant or above 150 bpm in an older child signals a potentially serious problem. Unusually slow rates, typically below 60 bpm in any child, also warrant immediate attention. Understanding the normal ranges by age is the fastest way to spot when something is off.
Normal Resting Heart Rate by Age
Children’s hearts beat faster than adults’ hearts because their hearts are smaller and need to pump more frequently to circulate blood. As a child grows, the resting rate gradually slows. Here are the typical resting ranges:
- Newborns (0–1 month): 100–160 bpm
- Infants (1–12 months): 100–150 bpm
- Toddlers (1–3 years): 90–140 bpm
- Preschoolers (3–5 years): 80–120 bpm
- School-age children (6–12 years): 70–110 bpm
- Teenagers (13–17 years): 60–100 bpm
These numbers apply when a child is calm and at rest. Crying, fever, physical activity, and anxiety all raise heart rate temporarily, and that’s completely normal. A toddler throwing a tantrum can easily hit 160 bpm or higher without anything being wrong. What matters most is the resting rate, measured when your child is sitting quietly or sleeping.
When a Fast Heart Rate Is Dangerous
A heart rate that stays elevated well above the normal range at rest is called tachycardia. In children, the threshold that concerns doctors varies by age, but a sustained resting rate above 220 minus the child’s age is a commonly used red flag for an abnormal rhythm. For a newborn, that means rates approaching or exceeding 220 bpm. For a 10-year-old, it’s around 210 bpm. These numbers point to a rhythm disturbance rather than a normal response to activity or stress.
The most common abnormal fast rhythm in children is supraventricular tachycardia (SVT), where the heart’s electrical signals take a wrong path and cause the heart to beat extremely fast, often 220–280 bpm in infants. SVT episodes can come and go, sometimes lasting seconds and sometimes hours. In short bursts, SVT isn’t usually life-threatening, but prolonged episodes can strain the heart because it doesn’t have time to fill with blood between beats. Infants are particularly vulnerable because they can’t tell you what they’re feeling, so signs like unusual fussiness, poor feeding, pale or grayish skin, and rapid breathing are what parents typically notice first.
Fever is the most common innocent cause of a fast heart rate in kids. A child’s heart rate rises roughly 10 bpm for every degree Fahrenheit of fever. So a 5-year-old with a temperature of 102°F might have a resting rate of 130 bpm, which looks high but is an expected response. The rate should come back down as the fever breaks. If it doesn’t, or if the rate seems disproportionately high for a mild fever, that’s worth investigating.
When a Slow Heart Rate Is Dangerous
An abnormally slow heart rate, called bradycardia, is less common in children than tachycardia but can be more immediately dangerous. A resting rate that drops below 60 bpm in any child is generally considered too slow. In infants, a heart rate under 100 bpm during waking hours is concerning, and anything below 60 bpm is a medical emergency because the heart may not be pumping enough blood to the brain and organs.
There’s one important exception: athletic teenagers. Highly trained young athletes can have resting heart rates in the 50s or even high 40s, just like adult endurance athletes. This is a sign of a strong, efficient heart, not a problem. The distinction is that these kids feel perfectly fine, have no dizziness or fainting, and their heart rate rises normally with exercise.
Dangerous bradycardia in children sometimes results from heart block, a condition where electrical signals between the upper and lower chambers of the heart are delayed or interrupted. It can be present at birth or develop after heart surgery or certain infections. Signs include fatigue, dizziness, fainting, and exercise intolerance.
Warning Signs Beyond the Number
A heart rate reading on its own doesn’t always tell the full story. How your child looks and acts matters just as much as the number on a pulse oximeter or fitness tracker. A child whose heart rate is 160 bpm but who is running around the playground is fine. A child whose heart rate is 160 bpm while sitting on the couch watching TV is not.
Symptoms that suggest a dangerous heart rate include:
- Fainting or near-fainting: The brain isn’t getting enough blood.
- Chest pain or pressure: Especially during rest or light activity.
- Visible difficulty breathing: Fast breathing that doesn’t match the child’s activity level.
- Pale, grayish, or bluish skin: A sign of poor circulation.
- Sudden fatigue or inability to keep up with peers: Especially if this is a change from their usual behavior.
- Complaints that the heart is “fluttering” or “skipping:” Older children can often describe palpitations.
In infants, the signs are subtler. Poor feeding, excessive sleepiness, and irritability are sometimes the only clues that something is wrong with the heart rhythm.
How to Check Your Child’s Heart Rate
The simplest method is to feel your child’s pulse at the wrist (on the thumb side) or at the neck (just beside the windpipe). For infants, the easiest spot is the inside of the upper arm, between the elbow and shoulder. Count the beats for 15 seconds and multiply by four to get beats per minute.
Timing matters. Check the rate when your child has been sitting or lying still for at least five minutes. Right after play, a bath, or crying will give you a misleadingly high number. If you’re tracking heart rate because of a concern, check it at different times of day over several days to look for patterns rather than relying on a single reading.
Pulse oximeters that clip onto a finger will also display heart rate, and many are accurate enough for home use. Smartwatches and fitness trackers designed for kids can give a general picture but aren’t medical-grade devices, so use them as a starting point rather than a diagnosis.
What Causes Abnormal Heart Rates in Children
Most episodes of fast heart rate in kids have a harmless cause: fever, dehydration, pain, anxiety, or caffeine from soda and energy drinks. These resolve when the trigger is addressed. Energy drinks are a particularly common and underrecognized culprit in school-age children and teens, with some containing 200–300 mg of caffeine per can, enough to push a child’s heart rate well above normal and occasionally trigger abnormal rhythms.
Structural heart defects present from birth can cause both fast and slow abnormal rhythms. So can certain genetic conditions that affect the heart’s electrical system, such as long QT syndrome and Wolff-Parkinson-White syndrome. These conditions sometimes run in families. A history of unexplained fainting or sudden cardiac death in a close relative raises the suspicion that a child’s heart rate abnormality could be inherited.
Other medical causes include anemia (low red blood cells force the heart to beat faster to deliver oxygen), thyroid disorders, and infections that inflame the heart muscle. Certain medications, including some used for asthma and ADHD, can also raise heart rate as a side effect.
What Happens During Evaluation
If your child’s heart rate is consistently outside normal range or they’re having symptoms, the first step is usually an electrocardiogram (ECG), a painless test that takes about five minutes and records the heart’s electrical activity. This alone can identify many rhythm disorders.
If the ECG is normal but symptoms come and go, your child may wear a portable heart monitor for 24 hours to several weeks. This captures what the heart is doing during everyday life, including sleep, school, and physical activity. For older kids, the monitor is roughly the size of a small phone and clips to a waistband or hangs from a lanyard.
Many childhood heart rhythm problems are highly treatable. SVT, the most common abnormal fast rhythm, responds well to simple techniques like bearing down or putting a cold washcloth on the face, which stimulate the vagus nerve and can reset the rhythm in seconds. When those don’t work, or when episodes are frequent, treatment options range from daily medication to a one-time procedure that permanently corrects the faulty electrical pathway, with success rates above 95% in experienced centers.